Is it biphobic?

No, it's not.
There are lots of people who are attracted to 2 or more genders who identify as gay or lesbian, and it's perfectly okay.
Hope this helps! <3

 

How you define yourself is ultimately up to you. If you feel more comfortable with calling yourself lesbian, then go for it--no one can tell you otherwise.

I think when it comes to biphobia, the root comes down to misconceptions about bisexuality. So unless your reason for not wanting to identify as bi stems from a stigma towards bisexuals or bisexuality, then no, it's not biphobia.

Edit: This is coming from someone who had some internalized biphobia of her own long before she accepted and claimed the label. So even if that's the case, try not to be too hard on yourself; we all have things we need to work through, and it certainly wouldn't make you a bad person if you were struggling with some internalized issues.

 

It's all up to you how you feel at the end of the day. Either way if you figure out you're a lesbian or bisexual is totally okay and it's fine to label yourself as one but realize you're the other down the road.
When it comes to biphobia, usually internalized biphobia comes from society's stereotypes of what a bisexual is. Usually society thinks bisexual people (mainly women) are 'greedy' or 'confused' which neither thing is true. Besides bisexuality is such a broad spectrum in and of itself. Some bisexuals are more attracted to one sex or another or evenly attracted to both. Also, if you only prefer women and dating them and you figure out you are bisexual, you don't have to date men. Your dating choices are all up to you and pursuing same-sex relationships with other women is a totally valid option.

 

I'll be frank: "biphobia" not the word, "erasure" might be. Depends on why you feel more comfortable with the label.